Evidence for ape intelligence got a major boost in the 1960s in Gombe, Tanzania, when Jane Goodall observed chimpanzees using a twig to "fish" for ants (pictured in a file photo)—the first documentation of wild chimps making and using tools. Until then, toolmaking had been considered a uniquely human ability.

The "notion is [tool use] requires higher intelligence, because it requires refashioning what nature has provided to achieve the user's goal," Anne Russon, an expert in ape intelligence at Canada's York University, said via email.

Since the toolmaking discovery, scientists have discovered our closest cousins can use sign language, hunt with spears of their own making, and even beat college students in basic memory tests, among other skills.

Added York University's Russon: "The great leap forward was using manual signs rather than vocal sounds for language—important because great apes don't have the same control over sound creation as humans do."

Photograph from Bettmann/Corbis

Ape Learns Words Like a Human

Researcher Sue Savage-Rumbaugh hugs Kanzi, star pupil of the Language Research Center in Atlanta, after the bonobo scored excellent results on a language comprehension and syntax quiz.

Kanzi, born in 1980, is "the world's undisputed ape-language superstar," according to the website of the Great Ape Trust, a research facility in Iowa that studies ape language and intelligence.

That's because he was the first ape to acquire language as children do: by being exposed to it.

Kanzi is also the first ape to show receptive understanding of spoken English and excels in research using novel sentences—phrases that require the learning of specific responses, the website said.

Syntax is more difficult to learn than individual words because it implies some understanding of relations between entities—ie. not just any old fruit, my mom's fruit, Russon noted.

The orangutan Azy selects a symbol for "apple" after being shown a slice of apple by a researcher at the Think Tank facility at Washington, D.C.'s National Zoo in 1996.

"Not only does Azy communicate his thoughts with abstract keyboard symbols, he also demonstrates a 'theory of mind' (understanding another individual's perspective) and makes logical, thoughtful choices that show a mental flexibility some chimpanzees lack," according to National Geographic magazine.

As part of the facility's Orangutan Language Project, orangutans, rewarded with food, learn to use a symbol-based language presented on a computer monitor, according to the Think Tank website.

The zoo's "dictionary" has about 70 abstract symbols, all of which have no visual relation to the object they represent. There are seven categories of symbols: food, proper names of people, verbs, adjectives, Arabic numbers, nonfood objects, and proper names of orangutans.

Though it wasn't the first time an ape had commuicated via symbols, Azy's accomplishment "meant a nonhuman species could attribute meaning to otherwise meaningless arbitrary symbols," Russon said.

An adult female lowland gorilla in the Republic of the Congo's Nouabalé-Ndoki National Park uses a walking stick to gauge the water's depth in a file picture. The behavior, documented in a 2005 study in the journal PLoS Biology, was the first evidence that wild gorillas use tools.

Previously, chimpanzees, bonobos, and orangutans had all been observed using tools. But scientists had speculated that gorillas had lost such skills out of lack of necessity, according to the study. After all, gorillas, the largest of the great apes, can easily crush nuts with their teeth or smash termite mounds without needing tools.

Overall, the walking-stick "observations suggest that the intelligence required for tool use evolved before the gorilla lineage split off from humans and the other great apes—providing further evidence that intelligence is not unique to humans," according to the synopsis of the study.

Indeed, "gorillas have tended to be considered the least smart of the great apes, so this is good, because it brings them into the fold," Russon said. Even so, "I don't think [gorillas using tools] is a major leap forward—they do it in zoos, and even monkeys use stick tools."

Ape researcher Jill Pruetz holds a spear made by a chimpanzee in 2007.

Pruetz, who receives funding from he National Geographic Society's Committee for Research and Exploration, was part of a team in Senegal that made the first ever scientific observations of chimpanzees making and using tools to hunt other mammals. (National Geographic News is part of the National Geographic Society.)

The researchers documented wild chimpanzees fashioning sticks into "spears" to hunt small primates called lesser bush babies (bush baby photo) no fewer than 22 times in 2007.

The apes' behavior shows "problem-solving at very high levels—like hunter-gatherers," said the Wildlife Conservation Society's Breuer, whose work has also been funded by the National Geographic Committee for Research and Exploration.

The discovery is "important because ancestral humans supposedly did this to kill meat, to fuel their stomachs and their large brains," Russon said.

The chimpanzee Ayumu begins a memory test with numerals jumbled on a touch screen in 2007.

Researchers at the Primate Research Institute in Kyoto, Japan, pitted young chimpanzees against human adults in two tests of short-term memory. Overall, the chimps won (watch ape-memory video).

That challenges the belief of many people, including a number of scientists, that "humans are superior to chimpanzees in all cognitive functions," researcher Tetsuro Matsuzawa of Kyoto University told the Associated Press in 2007.

Matsuzawa, a pioneer in studying the mental abilities of chimps, said even he was surprised.

The Wildlife Conservation Society's Breuer noted that "great apes are better in those memory tasks than humans—their memory functions in a very different way, and much faster than humans'."